Y2K Game
Source: USAMO 1999 Problem 5
October 3, 2005
USA(J)MOUSAMOalgorithmcombinatoricsgamegame strategy
Problem Statement
The Y2K Game is played on a grid as follows. Two players in turn write either an S or an O in an empty square. The first player who produces three consecutive boxes that spell SOS wins. If all boxes are filled without producing SOS then the game is a draw. Prove that the second player has a winning strategy.